1. Field of the Invention
My invention relates to pipe stoppers and, more particularly, to high pressure pipe stoppers which will not damage the inner surface of the pipe under test and which can be easily removed from a pipe once the test is completed.
2. Description of the Prior Art
The use of pipe stoppers in testing pipes, tubing, boilers, heat exchangers and other types of pressure vessels is well established in the art. For example, in testing a length of pipe for structural integrity and the ability to withstand a particular pressure, the entire length of pipe is sealed at both ends by an appropriate stopper and hydrostatic pressures are introduced through the pipe stopper.
A typical prior art high pressure pipe stopper includes a stem that terminates in a mandrel which is surrounded by a plurality of steel grips. The grips are provided with a sloped inner surface and by moving the grips up the sloped surface of the mandrel, typically sloped at an angle of 15.degree.-20.degree. or more, the grips are brought into contact with the inner surface of the pipe. Serrations on the outer surface of the grips provide positive engagement with the pipe. A threaded nut moves the grips, either directly or through a contact washer or the like; and holds the grips securely in place until the testing is completed. Since both ends of the pipe are closed, the stem of the pipe stopper includes a clearthrough passage for filling and venting. High pressure pipe stoppers of this type are shown in U.S. Pat. Nos. 2,855,003 and 4,381,800.
Pipe stoppers are commonly used to test lengths of metal pipe, such as pipe made from titanium, prior to its installation in military aircraft. This titanium pipe is subjected to testing under rather high pressures, upwards of 15,000 psi, and the use of pipe stoppers having serrations on the grips has been necessary in order to function under these high pressures. However, the serrations dig into the pipe and damage the inner surface of the pipe at each end. Before the tested pipe may be installed, it becomes necessary to cut off the damaged ends of the pipe. The use of such prior art pipe stoppers results in the waste of up to three inches or more in length from each end of the pipe and is, obviously, not desired.
Accordingly, it is an object of the present invention to provide a pipe stopper which will withstand high pressures but will not significantly damage the inner surface of the ends of the pipe under test.
For a pipe stopper to function at high pressures, a strong connection must be made between the pipe and the stopper itself. Often times the connection is so strong that the stopper cannot be easily removed by merely loosening the nut and pulling outwardly on the stem. Workers testing a section of pipe have often had to resort to striking the pipe stopper with a sledge hammer before the stopper became loose enough to remove. Such actions are generally harmful to the end of the pipe and result in more of the pipe being cut off and discarded.
Therefore, it is a further object of the present invention to provide a pipe stopper which can be easily removed from the end of a pipe without damaging the pipe.